UK light-heavyweight Buatsi earned a win yet underwhelming start to his career under new promoters with a points victory over Parker in the Manchester arena.
The Olympic bronze medallist's punch output appeared to earn him a majority decision in a tight ten-round fight at the boxing arena.
But Parker landed significant shots, delivering effective individual punches in a fight where the styles didn't complement each other, with constant grabbing marring the fight.
Two judges had it 96-94 in favor to Buatsi, with the remaining official a 95-95 draw.
"It wasn't my best performance but what defines champions? They win," Buatsi commented in the arena as he was faced disapproval from the crowd.
The Londoner returned to winning ways after his maiden career setback - an memorable fight with Callum Smith in last winter - to claim a 20th pro success.
Some ringside observers believed Parker, thirty-one, deserved the decision but the contender endured the second setback of his 28-match professional journey.
The Champion Secures Triumph in Slow Affair
The fighter's advancement has slowed in the past few years through management issues and extended periods of inactivity.
Previously predicted as the rising talent of UK boxing, he now finds himself trying to fulfil that early promise - maybe in what seems like a last chance - under new promotional backing.
He began cautiously, with both competitors willing to take risks in a cagey initial rounds.
The challenger, whose sole prior loss came at the lower weight class against his former opponent in two years ago after damaging his hand in the contest, was competing in only his second appearance at light-heavyweight.
By the halfway stage, Parker had made it competitive, creating difficulties for the favorite, who operated with a protective stance to narrowly win the more effective periods.
The crowd's patience diminished because of frequent holding, with the challenger falling to the floor various instances during close exchanges.
The underdog finished the stronger, but many rounds were hard to judge. Although, previous titleholder the boxing analyst - working with the broadcast network - had it particularly wide for Parker, awarding Buatsi just a single round.
Buatsi advances, but with the likes of heavy hitter David Benavidez, and Russian champion Dmitry Bivol leading the category, the road to world glory - based on this performance - still looks steep.
Hatton Memorial Fuels Manchester Derby Contest
In the supporting bout, Lyndon Arthur defeated Bradley Rea by divided decision in a outstanding local rivalry battle to win the European light heavyweight belt.
The venue became quiet for a profoundly moving memorial ahead of the contest as a bell ceremony tolled in memory of local hero Ricky Hatton, who died aged 46 in September.
It was the initial significant broadcast match card in the location since Hatton's death. As the last bell faded, the stillness became a chant of "there's just one Hatton".
The competition within the ring equaled the emotion. The eventual winner was sent to the canvas by a left hook squarely on the jaw in the early round, standing uncertainly to his feet on the count of eight.
But the traditional red shorts of Arthur soon advanced again. On the opposite side, Rea - in opposing blue - was injured soon, noticeable damage appearing under his orbital area as the fighters exchanged powerful shots.
The challenger, 27, delivered effective strikes but Arthur, 34, fought fire with fire with effective uppercuts as the pace rarely dropped over 12 rounds.
The victor edged the decision with official scores of draw, close margin and 115-112, but both fighters were persistent and full of heart, everything their inspiration Hatton represented.
